Wideband full stokes vector polarization detection chip based on double-layer grating structure

Abstract

A kind of wideband full stokes vector polarization detection chip based on double-layer grating structure, including the lower substrate of high light transmission medium, 4 different vibration direction metal wire grating of 2x2 array arrangement are arranged in lower substrate;There is also the upper substrate of high light transmission medium combined in reverse way with lower substrate, the upper substrate is provided with a medium wire grid, and its function is equivalent to wideband quarter-wave plate;Medium wire grid and one of the metal wire grating of lower substrate are coincident, the included angle between medium wire grid and metal wire grating is 45 ° or 135 ° angle, for realizing the detection of circular polarization state;Three metal wire grating on the lower substrate is used to realize the detection of three different linear polarization state.The present application adopts three metal wire grating to detect three linear polarization state, one metal wire grating and one medium wire grating are combined to detect circular polarization state, and full stokes vector measurement is realized.The volume surrounded by the corresponding four polarization states on Poincare sphere is not less than 1 / 6 times the cube of ball radius.

Description

Technical Field

[0001] This invention belongs to the field of optical polarization detection technology, and relates to polarization chips for the detection and processing of polarization images, specifically a broadband full Stokes vector polarization detection chip based on a double-layer grating structure. Background Technology

[0002] As an electromagnetic wave, light's polarization characteristic is another important property besides amplitude, wavelength, and phase. Under natural conditions, due to differences in structural properties, material types, surface roughness, and texture features among different objects, light undergoes polarization state changes during reflection, transmission, or scattering at the object's surface, which are significantly correlated with the object's characteristics. These changes typically contrast sharply with the polarization background of the surrounding environment. Therefore, introducing polarization detection technology into imaging systems can integrate multi-dimensional information such as target intensity and polarization state, enhancing the difference between the detected target and the environmental background, thus improving the ability to detect and identify targets. This technology has wide-ranging applications in industrial inspection, environmental monitoring, biomedicine, and optical remote sensing.

[0003] Polarization chips are the core component for realizing polarization detection technology. Traditional polarization chips, based on grating theory, generate metal wire grids with transmission directions of 0°, 90°, 45°, and 135° on a substrate medium. This metal wire grid structure can achieve linear polarization detection with high transmittance, large bandwidth, and high extinction ratio, and is a commonly used solution in the field of polarization detection technology. However, this structure cannot detect and extract circular polarization components in principle, and therefore cannot reconstruct the full Stokes vector of the target under test. Summary of the Invention

[0004] To address the technical problem that existing polarization detection elements cannot extract circular polarization components, the present invention aims to provide a broadband full Stokes vector polarization detection chip based on a double-layer grating structure, which can achieve full polarization information acquisition in the visible light band and effectively suppress noise, thereby further improving the detection and recognition capabilities of polarization imaging systems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A broadband all-Stokes vector polarization detector chip based on a double-layer grating structure includes a lower substrate of a high-transmittance medium, on which four metal wire grids with different transmission directions are arranged in a 2×2 array; characterized in that it also has an upper substrate of a high-transmittance medium that is inverted and bonded to the lower substrate, on which a dielectric wire grid is provided, which is functionally equivalent to a broadband quarter-wave plate; the center of the dielectric wire grid coincides with that of one of the metal wire grids on the lower substrate, and the dielectric wire grid and the metal wire grid that coincides with the center form an angle of 45° or 135°, which is used to realize the detection of circular polarization state; the other three metal wire grids arranged on the lower substrate are used to realize the detection of three different linear polarization states.

[0007] According to the present invention, the dimensions of the individual metal wire grid and dielectric wire grid are 100 μm × 100 μm, wherein:

[0008] The metal grid has a thickness of 110 nm, and the dielectric grid has a thickness of 640 nm. The periods of both the metal grid and the dielectric grid are less than the wavelength. The dielectric grid is made of silicon nitride, and the metal grid is made of aluminum.

[0009] Specifically, the materials of the high-transmittance upper and lower substrates are both silicon dioxide, with a thickness of 750 μm.

[0010] The metal wire grids are arranged in a comb-like pattern on the surface of the lower substrate, with a period of 150 nm. The spacing and width between the wire grids are equal.

[0011] The dielectric grids are arranged in a comb-like pattern on the surface of the upper substrate, with a period of 256 nm. The spacing and width between the dielectric grids are equal.

[0012] The distance between the upper and lower bases after the inverted combination is 0.9 mm.

[0013] The metal wire grid has a height of 110 nm, a width of 75 nm between wire grids, and a duty cycle of 50%.

[0014] The dielectric grid has a grid height of 640 nm, a grid width of 164 nm, and a duty cycle of 64%.

[0015] The fast and slow axes of the dielectric grid are along the grid direction and perpendicular to the grid direction, respectively.

[0016] The arrangement of the four metal wire grids on the upper substrate and the one dielectric wire grid on the lower substrate corresponds to the volume of the tetrahedron formed by the four polarization states detected on the Poincaré sphere, which is not less than 1 / 6 (the Poincaré sphere has a radius of 1).

[0017] This invention relates to a broadband all-Stokes vector polarization detector chip based on a double-layer grating structure. The chip is formed by arranging a metal wire grating and a dielectric wire grating. The light to be measured is incident from the metal wire grating end, resulting in four linearly polarized states. One of these linearly polarized lights then passes through the dielectric wire grating. Because its polarization direction forms an angle of 45° or 135° with the fast and slow axes of the dielectric wire grating, this linearly polarized light is converted into circularly polarized light with the corresponding rotation direction and emitted. The other three linearly polarized lights retain their original polarization states. The all-Stokes vector parameters of the original incident light can be obtained by calculating the three linearly polarized lights and the circularly polarized light with one rotation direction. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the principle of the broadband all-Stokes vector polarization detector chip based on a double-layer grating structure of the present invention.

[0019] Figure 2 This is a schematic diagram of the metal wire grid and dielectric wire grid dimensions of the broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure of the present invention.

[0020] Figure 3 This is a schematic diagram of the broadband full Stokes vector polarization detection chip structure based on a double-layer grating structure and its inverted sealing.

[0021] Figure 4 This is a schematic diagram of the energy coupling model of a double-layer grating. In the diagram, (a) is a schematic diagram of the energy coupling model, and (b) is a curve showing the relationship between coupling efficiency and bonding distance.

[0022] Figure 5 This is a schematic diagram of a metal wire grid structure.

[0023] Figure 6 These are the polarization characteristic curves of the metal wire grid. Among them, (a) is the transmittance curve for two polarization directions, and (b) is the extinction ratio curve.

[0024] Figure 7 This is a schematic diagram of a dielectric grid structure.

[0025] Figure 8 These are the polarization characteristic curves of the dielectric wire grid. Among them, (a) shows the transmittance curves for the TM and TE polarization directions, and (b) shows the phase curves for the TM and TE polarization directions.

[0026] Figure 9 It is the phase difference curve of the fast and slow axes of the dielectric grid.

[0027] Figure 10 This is a schematic diagram of the arrangement of metal wire grids and dielectric wire grids.

[0028] Figure 11 This is a schematic diagram of two polarization detection state detection methods in Example 2.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0030] It should be noted that the following descriptions of the embodiments are merely exemplary, and the present invention is not limited to the following embodiments. In the following detailed description, numerous details are set forth to facilitate explanation and provide a comprehensive understanding of the technical solutions of the present invention. However, it is apparent that one or more of the following embodiments can be implemented without these specific details. Furthermore, in the following description, descriptions of well-known technologies are omitted to avoid unnecessarily obscuring the concepts of the present invention.

[0031] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0032] In this embodiment, the metal wire grating and dielectric wire grating refer to subwavelength wire gratings. A typical arrangement of traditional metal wire gratings (subwavelength) is two pairs of orthogonal directions. The applicant's research has found that, based on achieving high transmittance, large bandwidth, and high extinction ratio linear polarization detection, introducing a double-layer grating structure can solve the problem of the inability to extract circular polarization components in existing polarization detection chips, achieving broadband full Stokes vector detection and reconstruction, while simultaneously utilizing combinations of different detection polarization states to achieve noise suppression.

[0033] The applicant developed a broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure, with an operating wavelength of 450nm–650nm. Metal wire gratings and dielectric wire gratings are grown on highly transparent dielectric substrates; the structure includes metal wire gratings, dielectric wire gratings, and a highly transparent dielectric substrate; wherein the metal wire gratings and dielectric wire gratings are grown on highly transparent dielectric substrates. The function of the metal wire gratings is to extract linearly polarized light, arranged in a 2×2 array layout. The transmission directions of each metal wire grating are 0°, 90°, 45°, and 135°, and the orthogonal transmission directions are distributed along the diagonal of the 2×2 array. The dielectric wire grating functions equivalent to a broadband quarter-wave plate, and when used in conjunction with a metal wire grating, it can extract circularly polarized light.

[0034] This broadband full-Stokes vector polarization detector chip, based on a dual-layer grating structure, can be used as a unit in a focal plane full-polarization camera target array. Its schematic diagram is shown below. Figure 1As shown, the light to be tested, 01, is incident from one end of a dielectric grating, resulting in polarized light 05 (0° with line 04), 07 (90° with line 06), and 03 (135° with line 02). Simultaneously, after passing through the dielectric grating, the incident light becomes natural light 08, which contains a circularly polarized state 09 with an unknown direction. This natural light 08, containing the circularly polarized state 09, then continues to pass through a metal grating. Because its transmission direction forms a 45° angle with the major axis 010 and minor axis 011 of the dielectric grating, the circularly polarized light 09 in this mixed state is filtered and converted into linearly polarized light 012, which is then emitted. The other three linearly polarized lights retain their original polarization states. By calculating the three linearly polarized lights and one circularly polarized light, the total Stokes vector parameters of the original incident light can be obtained.

[0035] The following were determined during the research and development process:

[0036] The dielectric grid and one of the metal grids are bonded together using an inverted snap-fit ​​method, wherein the centers of the dielectric grid and the single metal grid are aligned vertically and form an angle of 45° or 135°. This enables the detection and extraction of circularly polarized light.

[0037] The metal grid is made of aluminum; the dielectric grid is made of silicon nitride; and the upper and lower substrates of the high-transmittance dielectric are both made of silicon dioxide.

[0038] The metal wire grids are arranged in a comb-like pattern on the surface of the highly transparent dielectric substrate. The period is 150 nm, and the spacing between the wire grids is equal to the width of the wire grids.

[0039] The metal wire grid has a wire grid height of 110 nm, a wire grid width of 75 nm, and a duty cycle of 50%.

[0040] The dimensions of each individual metal wire grid and dielectric wire grid are 100 μm × 100 μm. The spacing between the four metal wire grids arranged on the lower substrate is 200 μm.

[0041] The dielectric grids are arranged in a comb-like pattern on the surface of the upper substrate, with a period of 256 nm. The spacing and width between the grids are equal. The grid height is 640 nm, the width between grids is 164 nm, and the duty cycle is 64%. Its major axis and minor axis (fast and slow axes) are parallel and perpendicular to the grid direction, respectively.

[0042] Furthermore, to improve noise suppression (Gaussian noise) capability, the arrangement of dielectric and metal wire grids must satisfy certain relationships. Three metal wire grids detect three linearly polarized states (corresponding to three points on the equator of the Poincaré sphere), and one metal wire grid and one dielectric wire grid jointly detect one circularly polarized state. Either left-handed or right-handed circularly polarized states are acceptable (left-handed circular polarization is located at the north pole of the Poincaré sphere, and right-handed circular polarization is located at the north pole of the Poincaré sphere). The larger the volume of the tetrahedron formed by the vertices of these four detected polarization states, the better. To ensure that the noise weight is no higher than 4, the volume of the tetrahedron formed by the four detected polarization states on the Poincaré sphere is no less than 1 / 6 (the radius of the Poincaré sphere is 1). Since there are three linearly polarized detection states in the chip, the maximum volume cannot exceed [a certain value].

[0043] The following are specific embodiments provided by the inventor.

[0044] Example 1:

[0045] This embodiment presents a broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure, and the dimensions of its metal wire grating and dielectric wire grating are shown in the figure below. Figure 2 As shown. The dimensions of a single metal grid and dielectric grid 7 are 100μm × 100μm. One dielectric grid 7 is arranged on the upper substrate 1, and the spacing between the four metal grids (3, 4, 5, 6) arranged on the lower substrate 2 is 200μm.

[0046] The structure and inverted bonding of the broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure are shown below. Figure 3 As shown, the device includes four metal wire grids (3, 4, 5, 6), one dielectric wire grid 7, and upper and lower substrates (1, 2) with high transmittance. The four metal wire grids (3, 4, 5, 6) are made of aluminum with a thickness of 750 μm. This is because aluminum has a flat, wide bandwidth in the 450 nm–650 nm visible light wavelength range, and its fabrication process is relatively mature. The dielectric wire grid 7 is made of silicon nitride because it provides sufficient phase delay in the 450 nm–650 nm visible light wavelength range, which is beneficial for the design of micro / nano phase devices. The upper and lower substrates (1, 2) with high transmittance are made of silicon dioxide because silicon dioxide has high optical transmittance and a flat band within the 450 nm–650 nm visible light wavelength range, and it also has good material stability, making it a good substrate material in the visible light range.

[0047] like Figure 3As shown, four metal wire grids (3, 4, 5, 6) are arranged in a 2×2 array and grown on a high-transmittance dielectric substrate 2 according to the transmission directions of 0°, 90°, 45°, and 135°, respectively. The dielectric wire grid 7 functions equivalent to a quarter-wave plate, with its fast and slow axes along the wire grid direction and perpendicular to the wire grid direction, respectively. The dielectric wire grid 7 is also grown on a high-transmittance dielectric substrate 1.

[0048] The four metal wire grids (3, 4, 5, 6) are bonded (sealed) to the dielectric wire grid 7 using an inverted snap-fit ​​method (marked 8 in the figure). The dielectric wire grid 7 coincides with the center of one of the metal wire grids 6, and the directional angle between the dielectric wire grid 7 and the metal wire grid 6 that coincides with the center is 45° or 135°.

[0049] The inverted buckle 8 method specifically involves aligning the metal wire grid 6 with the dielectric wire grid 7 to avoid the influence of the upper and lower substrates (1, 2) of the dielectric on polarization modulation.

[0050] In this embodiment, the gap 9 between the upper substrate 1 and the lower substrate 2 after they are inverted and sealed determines the coupling efficiency of the polarization state intensity of the broadband full Stokes vector polarization detector chip based on the double-layer grating structure. For example... Figure 4 As shown in (a), due to the diffraction effect, the incident light 01 diverges 013 after passing through the dielectric grating 7, resulting in a decrease in the light intensity received by the metal grating 6. The received light intensity 014 is only a part of the total light intensity 015 modulated by the dielectric grating 7. The coupling relationship can be expressed as:

[0051]

[0052] Where Σ' and Σ represent the light intensity receiving surface and the light intensity distribution surface, respectively, and S' and S represent the area of ​​the dielectric grating and the current cross-sectional light intensity distribution area, respectively.

[0053] The relationship between coupling efficiency and the distance after bonding is as follows: Figure 4 As shown in (b), according to the applicant's experiment, when the bonding distance between the upper substrate 1 and the lower substrate 2 is within 0.9 mm, the coupling efficiency is not less than 80%. In this embodiment, the gap 9 after the upper substrate 1 and the lower substrate 2 are sealed is controlled within 0.9 mm.

[0054] In this embodiment, the design process of the metal wire grids (3, 4, 5, 6) is as follows: First, based on the subwavelength optics theory, combined with the material, function, working band and processing capability, the approximate range of the height, period and duty cycle of the metal wire grids (3, 4, 5, 6) is determined. Then, within the theoretical range, the design is optimized for light in both TM and TE polarization states using parameter scanning, with transmittance and extinction ratio as the criteria, and finally the final geometric structure of the wire grid is determined.

[0055] In this embodiment, the structural diagram of the four metal wire grids (3, 4, 5, 6) is shown below. Figure 5 As shown in the figure. The grid height h is 110 nm, the period P is 150 nm, the width l is 75 nm, and the duty cycle is 50%.

[0056] The polarization characteristic curves of the four metal wire grids (3, 4, 5, 6) are shown in [reference]. Figure 6 The transmittance curves for the two polarization directions are as follows: Figure 6 As shown in (a), the extinction ratio curve is as follows: Figure 6 As shown in (b).

[0057] The design process of dielectric grid 7 is as follows: First, based on subwavelength optics theory, combined with materials, functions, operating bands and processing capabilities, the approximate range of the height, period and duty cycle of dielectric grid 7 is determined. Then, within the theoretical range, the design is optimized for both TM and TE polarization states using parameter scanning. Unlike metal grids (3, 4, 5, 6), the criteria for dielectric grid 7 not only require high transmittance, but also strictly limit the constant phase difference between the two polarization states to ensure the broadband characteristics of dielectric grid 7. Finally, its geometric structure is determined.

[0058] The structure of the dielectric grid 7 is shown in the figure. Figure 7 As shown in the figure, the gate height h is 640 nm, the period P is 256 nm, the gate width l is 164 nm, and the duty cycle is approximately 64%.

[0059] The polarization characteristic curve of the dielectric grid is shown in [reference]. Figure 8 The transmittance curves for the TM and TE polarization directions are shown below. Figure 8 As shown in (a), the phase curves for the two polarization directions, TM and TE, are as follows: Figure 8 As shown in (b), the phase difference curve of the fast and slow axes is as follows: Figure 9 As shown.

[0060] The extinction ratio of the circularly polarized state of the broadband all-Stokes vector polarization detector chip based on a double-layer grating structure in this embodiment is calculated using the following formula:

[0061] Let the transmittance of the dielectric grid in the TM and TE polarization directions be t, respectively. x t y The phase differences are respectively The Jones matrix of the dielectric grid can then be written as:

[0062]

[0063] Let the Jones matrix of the incident light be [A1 B1]. T The Jones matrix of the emitted light is [A2 B2].T If the angle between the metal grid and the dielectric grid is θ, then:

[0064]

[0065] According to the definition of extinction ratio, which is the ratio of the intensity of the polarization state in the transmission direction to the intensity of the polarization state in the suppression direction, it can be written as:

[0066]

[0067] Among them, T 135° T 45° Let be the transmittance in the vibration transmission direction and the transmittance in the vibration suppression direction of the metal wire grid, respectively. Clearly, β represents the extinction ratio of the metal wire grating, so the extinction ratio of the circularly polarized state can be written as:

[0068]

[0069] Considering the symmetry of the Jones matrix, let's assume the incident light is left-handed circularly polarized, i.e. The angle θ between the metallic wire grid and the dielectric wire grid is 45°, and the extinction ratio β of the metallic wire grid is taken as... Figure 6 (b) Substituting the transmittance of the dielectric grid and the phase difference data into the above formula, the extinction ratio of circular polarization detection can be obtained. Table 1 below shows the extinction ratio of circular polarization detection of the polarization detection chip.

[0070] Table 1: Extinction ratio of circular polarization detection by polarization detection chip

[0071] wavelength / nm Extinction ratio 450 352.6979 475 432.0011 500 280.5906 525 219.4139 550 374.9713 575 768.9222 600 1245.5512 625 428.1604 650 296.3133

[0072] In this embodiment, the Mueller matrix M of the metal wire grid LP (θ) can be written as:

[0073]

[0074] in, denoted as the transmittance in the transmission direction of the metal wire grid. θ is the reciprocal of the extinction ratio of the metal wire grid, and θ is the angle between the transmission direction of the metal wire grid and the x-axis.

[0075] Let the Stokes vector of the incident light be S = [S0, S1, S2, S3]. T The Stokes vector after passing through the metal wire grid is S'=[S0',S1',S2',S3']. T Then the two satisfy:

[0076]

[0077] Where θ takes values ​​of 0°, 90° and 135° respectively.

[0078] The Mueller matrix M of the dielectric wire grid QWP (θ,δ) can be written as:

[0079]

[0080] in, For the fast axis transmittance of the dielectric grid, θ is the ratio of the transmittance of the slow axis to the fast axis of the dielectric grid, θ is the angle between the fast axis and the x-axis of the dielectric grid, and δ is the phase difference between the fast and slow axes.

[0081] Similarly, according to Figure 1 The physical process of circularly polarized light detection is described, and the Stokes vector transformation relationship of the incident light after passing through the dielectric wire grating and the metal wire grating satisfies:

[0082]

[0083] Based on the above model formula, the broadband full Stokes vector polarization detector chip based on a double-layer grating structure in this embodiment detects a new Stokes vector after modulating the incident light Stokes vector. in, ψ represents the angle between the transmission direction of the metal wire grid and the x-axis, and ψ represents the angle between the fast axis of the dielectric wire grid and the x-axis.

[0084] According to the calculation, S'(0°,0°), S'(90°,0°), S'(135°,0°), and S'(0°,45°) are obtained respectively.

[0085] In this embodiment, the full Stokes vector reconstruction is calculated in the following way:

[0086]

[0087]

[0088]

[0089]

[0090] When the incident light is x-axis polarized, i.e., the Stokes vector is S = [1, 1, 0, 0] T Table 2 below shows the full Stokes vector restoration results of the broadband full Stokes vector polarization detector chip based on a double-layer grating structure given in this embodiment.

[0091] Table 2: Incident light S = [1,1,0,0] T Full Stokes vector restoration results

[0092]

[0093] When the incident light is left-handed circularly polarized, i.e., the Stokes vector is S = [1, 0, 0, 1] T The results of the full Stokes vector restoration are shown in Table 3.

[0094] Table 3: Incident light S = [1,0,0,1] T Full Stokes vector restoration results

[0095]

[0096] When the incident light is superimposed with x-axis polarized light and left-handed circularly polarized light, i.e., the Stokes vector is S = [1, 1, 0, 1] T The broadband full Stokes vector restoration results of the broadband full Stokes vector polarization detector chip based on the double-layer grating structure in this embodiment are shown in Table 4 below.

[0097] Table 4: Incident light S = [1,1,0,1] T Full Stokes vector restoration results

[0098]

[0099] Example 2:

[0100] To achieve noise suppression, the inventors optimized the arrangement of the four metal grids (3, 4, 5, 6) and the dielectric grid 7. The schematic diagram is shown in 10(a). The characteristics (material, period, duty cycle, height) of the metal grids / dielectric grids are consistent with those of Example 1, only the arrangement is different.

[0101] Metal grids (3, 4, 5, 6) are arranged with transmission directions of 0°, 60°, 120°, and 90°, respectively. Dielectric grid 7 coincides with the center of metal grid 6, and the directional angle between dielectric grid 7 and metal grid 6 is 45°. When the light to be measured is incident on the chip, metal grids (3, 4, 5) complete the measurement of three linear polarizations, while metal grid 6 and dielectric grid 7 complete the measurement of left-handed circular polarization. The full Stokes parameter can be restored using the three linear polarizations and one circular polarization.

[0102] Note that the above arrangement is not unique. As long as the transmitted polarization states of three elements in the metal grid (3, 4, 5, 6) are uniformly distributed along the equator of the Poincaré sphere, and the transmitted polarization states of the remaining metal grid (e.g., metal grid 6) and the dielectric grid 7 are located at the south or north poles of the Poincaré sphere, then the arrangement is acceptable. Figure 10 As shown in (b).

[0103] The Gaussian noise weighting method for the broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure in this embodiment is as follows:

[0104] Gaussian noise exists in the output signals of all detectors and is independent of the signal being measured. Therefore, when Gaussian noise with a standard deviation of σ exists, its noise covariance matrix Γ n It can be represented as:

[0105] Γ n =σ 2 W - (W - ) T

[0106] Where W is the measurement matrix, it can be represented as:

[0107] W = 0.5T, denoted as

[0108] Among them, a i ,b i ,c i Let represent the coordinates of a point on the Poincaré sphere (i = 1, 2, 3, 4). The measurement matrix W contains 4 measurements, thus corresponding to 4 points on the Poincaré sphere. According to eigenvalue theory, we have:

[0109]

[0110] Where M is an orthogonal identity matrix that does not affect the measurement of Stokes parameters, and μ0, μ1, μ2, μ3 are the eigenvalues ​​of matrix T. Therefore, the total noise weight is:

[0111]

[0112] Where V is the volume of the tetrahedron formed by the measurement matrix at four points on the Poincaré sphere.

[0113] When the standard deviation of the detector's Gaussian noise is σ, the total noise weight for measuring the Stokes parameters is 2.621. Furthermore, when the transmission vibration of the metal wire grids (3, 4, 5) changes, causing the volume of the tetrahedron formed by the detector's polarization state to decrease, the total noise of the measurement decreases.

[0114] Figure 11 (a) and (b) represent two other polarization detection methods provided by the inventors. The transmission directions of the metal wire grids (3, 4, 5) are marked in the figures. The metal wire grid 6 and the dielectric wire grid 7 can perform circular polarization detection. The noise weights corresponding to them can be calculated as 3.526 and 3.043 respectively using the formula above.

[0115] It can be seen that the tetrahedral volume formed on the Poincaré sphere by the detection polarization states (A, B, C) of the metal wire grids (3, 4, 5) and the circularly polarized state (D) realized by the metal wire grids 6 and the dielectric wire grids 7 has a significant impact on the noise weight of the measured S-parameters.

[0116] Figure 11 (d) shows the relationship between noise weight and tetrahedral volume, where the solid line represents the theoretical limit of noise weight and the circle represents the actual noise weight of the corresponding measurement method. Therefore, in order to ensure that the chip in this embodiment has good noise immunity and that the measured noise weight does not exceed 4, the volume of the tetrahedron formed by the four polarization states detected on the Poincaré sphere is not less than 1 / 6 (the radius of the Poincaré sphere is 1).

Claims

1. A broadband all-Stokes vector polarization detector chip based on a double-layer grating structure, comprising a lower substrate of a high-transmittance medium, and four metal wire grids with different transmission directions arranged in a 2×2 array on the lower substrate; characterized in that, There is also an upper substrate with a high-transmittance medium that is inverted and bonded to the lower substrate. A dielectric grid is provided on the upper substrate, which is functionally equivalent to a broadband quarter-wave plate. The center of the dielectric grid coincides with that of one of the metal grids on the lower substrate. The dielectric grid and the metal grid that coincides with the center form an angle of 45° or 135° to realize the detection of circular polarization. The other three metal grids arranged on the lower substrate are used to realize the detection of three different linear polarization states.

2. The broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure as described in claim 1, characterized in that, The dimensions of each individual metal wire grid and dielectric wire grid are 100μm × 100μm, wherein: The metal wire grid has a thickness of 110 nm, and the dielectric wire grid has a thickness of 640 nm. The periods of both the metal grid and the dielectric grid are less than the wavelength. The dielectric grid material is silicon nitride, and the metal grid material is aluminum.

3. The broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure as described in claim 1, characterized in that, Both the upper and lower substrates with high light transmittance are made of silicon dioxide with a thickness of 750 μm.

4. The broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure as described in claim 1, characterized in that, The metal wire grids are arranged in a comb-like pattern on the surface of the lower substrate, with a period of 150 nm. The spacing and width between the wire grids are equal.

5. The broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure as described in claim 1, characterized in that, The dielectric grids are arranged in a comb-like pattern on the surface of the upper substrate, with a period of 256 nm. The spacing and width between the dielectric grids are equal.

6. The broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure as described in claim 1, characterized in that, The distance between the upper and lower bases after the inverted combination is 0.9 mm.

7. The broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure as described in claim 4, characterized in that, The metal wire grid has a wire grid height of 110 nm, a wire grid width of 75 nm, and a duty cycle of 50%.

8. The broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure as described in claim 5, characterized in that, The dielectric grid has a grid height of 640 nm, a grid width of 164 nm, and a duty cycle of 64%.

9. The broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure as described in claim 1, characterized in that, The fast and slow axes of the dielectric grid are along the grid direction and perpendicular to the grid direction, respectively.

10. The broadband all-Stokes vector polarization detector chip based on a dual-layer grating structure as described in claim 1, characterized in that, The arrangement of the four metal wire grids on the upper substrate and the one dielectric wire grid on the lower substrate corresponds to the volume of the tetrahedron formed by the four polarization states detected on the Poincaré sphere being no less than 1 / 6, and the radius of the Poincaré sphere is 1.

Images